Charlemagne spread Christianity throughout the Empire by going to war with many people. After defeating them, he gave them two choices: Christianity or death. Many chose Christianity, while other stayed faithful to their past religion. Because he "always kept his promises" he killed over 4,500 people.

Answer
Charlemagne used conquests and tyranny to spread Christianity.

Charlemagne used conquests and tyranny to spread Christianity.

Kathleen Jefferts Schori, presiding bishop of the U.S. Episcopal Church, said, "Charlemagne converted whole tribes by the sword." In the year 782, the Frankish king Charlemagne reputedly beheaded forty-five hundred Saxons who resisted his campaign of forced conversion to Christianity. In 800, the Pope crowned Charlemagne in Rome, as Holy Roman Emperor.